Long-lasting effect evoked by tonic muscle pain on parietal EEG activity in humans

Objective: To explore EEG changes evoked by tonic experimental muscle pain compared to a non-painful vibratory stimulus. Methods: Thirty-one EEG channels were recorded before, during and after pai nful and non-painful stimulation. Pain was induced in the left brachioradia lis muscle by injection of hypertonic (5%) saline. The vibratory stimulus w as applied to the skin area overlying the brachioradialis muscle. The power of the major frequency components of the EEG activity (FFT, fast Fourier t ransform) was quantified and t-maps between the different experimental cond itions were evaluated in frequency domain. Results: The main effect of muscle pain, compared to non-painful stimulatio n, was a significant and long-lasting increase of delta (1-3 Hz) power and an alpha-1 (9-11 Hz) power increase over the contralateral parietal locus. This finding could suggest a decreased excitability of the primary somatose nsory cortex during muscle pain. The main effect of vibration, compared to its unstimulated baseline, consisted in an increase of beta-1 (14-20 Hz) po wer in the right frontal region. Conclusions: Our data demonstrate significant and specific topographic EEG changes during tonic muscle pain. Since these modifications differ from tho se produced by an unstimulated baseline and during non-painful tonic stimul ation, they might reflect mechanisms involved in the processing of nocicept ive and adverse tonic stimuli. (C) 2000 Elsevier Science Ireland Ltd. All r ights reserved.